The invention relates to a laser arrangement for controlling the direction of a beam from a laser.
In many applications, it is desirable to be able to aim a laser, for example to make it sweep across large areas. Normally, the laser is mounted on a rotating table that can be swivelled to enable the laser to execute a sweeping motion. When the laser is to be used in an environment subject to jolting, the rotating table""s movement can be controlled by attachment to a gyro, thereby stabilizing the laser beam.
JP 09015526 A provides an alternative arrangement featuring a cone-shaped mirror asymmetrically arranged on an axle. The axle itself can in turn be rotated using a motor. A steadily directed laser beam hitting the surface of the mirror will, because of the asymmetry, be reflected in a direction dependent on the angle of the axle. Consequently, this arrangement allows for the possibility of sweeping the mirror-reflected laser beam through a full 360xc2x0 by rotating the axle one complete revolution.
According to one aspect of the invention in question, this device provides a laser arrangement with the means to steer the laser beam across a reflecting body, which is in turn designed to reflect the said laser beam so that it is aimed in a surrounding space within an area, which from the reflecting body covers at least a part of a circular rotation in the instrument plane, as well as an angle interval of approximately xc2x160xc2x0 in relation to the instrument plane. The device is characterised in that the steering mechanism is arranged in the path of the beam between the laser and the reflecting body, and it is designed to direct the laser beam, within the area, according to a pre-selected direction of the reflected beam. The steering mechanism in the device comprises a spatial light modulator (SLM), whose phase-shift pattern determines the modulating angle from the light modulator.
The light modulator""s phase-shift pattern alters the modulating angle by shifting the phase at different points across the cross-section of the beam by different amounts depending on the desired modulation of the beam. For example, etched glass plates can be used for altering the phase front of a laser beam. These patterned plates are called kinoforms.
The reflecting body can have a number of different shapes. By allowing the laser beam to sweep across the envelope surface of a cone or truncated cone, it is possible to reflect the laser beam in the surrounding space within an area that from the envelope surface in the instrument plane comprises a circular loop as well an angle interval of approximately xc2x145xc2x0 to the instrument plane. This possible area of reflection can be achieved without having to turn the laser itself. Approximately the same possible reflecting area could be obtained using an essentially hemispherical reflecting body. This reflecting area could be somewhat larger by using reflecting bodies with other shapes, for example a parabolic-shaped reflecting body, or a wide-angled lens.
It is preferable for the steering mechanism to contain some calculating unit arranged to calculate the direction of the beam in relation to the pre-selected direction, as well as calculate the phase-shift pattern settings of the light modulator accordingly. It would also be preferable for the phase-shift pattern to be calculated so that aiming in the chosen direction is achieved without any significant loss of strength.
The limit of the light modulator""s image-update speed is about 10 kHz. It is therefore possible with the help of a spatial light modulator to direct the laser beam in up to 10,000 directions per second anywhere within the above-mentioned area. Using a spatial light modulator means that none of the device""s components contain any moving parts, facilitating a very long life expectancy for the device, and low manufacturing and maintenance costs.
By using the light modulator above, it is possible to steer the beam in such a way so as to inhibit the occurrence of beam divergence at the reflecting body. The calculating unit is arranged to instruct the light modulator to reshape the laser beam""s wave front so as to avoid the occurrence of beam divergence.
For applications in environments exposed to movement and vibration, it can be of considerable advantage if the laser, light modulator and reflecting organ are all firmly fixed in a system together with a movement-detection device, such as a gyro. In this embodiment, on calculating the beam direction, the steering mechanism is designed to compensate for movement in the system detected by the gyro. The system can therefore be stabilized without the need for moving parts such as a rotating or stabilizing table. This produces considerable cost savings in design, manufacture and maintenance.